1. Field of the Invention
This invention relates generally to waste treatment, and more particularly relates to a composition for the treatment of sewage containing biological solids. The composition reduces the difficulties and dangers of handling the treatment material, more rapidly becomes highly active thereby improving the capacity of the treatment facility and provides a resulting liquid or solid product of the treatment process which is suitable for application to soil used for agricultural purposes.
2. Description of the Related Art
The prior art discloses a wealth of materials and processes for treating waste, such as waste water and sewage. Alkaline materials, including lime, have been used for treating the biological solids in municipal and industrial waste water treatment plants. Such treatments are shown, for example, in U.S. Pat. Nos. 5,186,840 and 4,415,467. High alkalinity destroys potentially harmful pathogenic microbes by raising the pH of the host material to a level at which the microbes cannot survive. Federal regulations require that biosolid materials be brought to and held at a pH level of 12 for at least 2 hours and at a pH level of 11 for an additional period of at least 22 hours to assure the destruction of the pathogens.
Although the prior art teaches treating waste water with lime, there are problems associated with the prior art methods and compositions used for such treatments. The problems are a combination of:
(1) the difficulty of mixing the lime into the sewage and the cost for equipment to assist in the mixing; PA1 (2) the dangers to human health and property from the use of dry particulate lime; PA1 (3) the slow speed of the activation of the lime in raising the pH and destroying the pathogens after it is applied, which results in a slow down of the treatment process and therefore reduces the capacity of the treatment facility; and PA1 (4) the inclusion of materials in the treated biological, solid products of the sewage treatment process which are not suitable for application to soil used for agricultural purposes.
Conventionally, dry quicklime, CaO, or hydrated lime, Ca(OH).sub.2, also known as slaked lime, is delivered to a waste treatment plant in bulk or in bags, or similar containers. The lime is dumped into the biosolids treatment tanks, which results in a large proportion of the lime sinking to the bottom as a mass which tends to stick together and is difficult to break up. Attempts to break it up are both difficult and time consuming with dispersement of the lime being non-homogeneous and incomplete. Because of the difficulty of dispersing lime under such conditions, the throughput capacity of the sewage treatment plant is reduced.
One approach to solving this problem is to install new, additional equipment to speed up the dispersion of the lime and more rapidly initiate the activity of the lime. This, however, requires a major, capital investment. An example is found in U.S. Pat. No. 4,110,211. As a consequence, it is costly to achieve the above pH levels required by federal regulation.
Additionally, dry lime is a caustic material and readily disperses into the air, making it both messy and dangerous to handle and irritating to workers. Workers may breathe in the lime or get it on their skin, in their eyes or on their clothing, creating a potential for causing discomfort, injury or illness. In windy weather conditions, the lime particles may also be carried onto neighboring areas, creating a potential for damage to property and the environment.
The prior art has recognized that it would be desirable to supply lime to a sewage treatment facility by means of a tanker in the form of an aqueous suspension (a slurry) in order to make the lime easier and safer to handle and to apply into the treatment process. However, lime which is mixed in water settles and agglomerates as deposits at the bottom of the container, and therefore requires continued or periodic stirring or agitation to keep it suspended and dispersed. This requires an investment in additional equipment to maintain the suspension during storage and transportation, although it eliminates the need for an investment in equipment at the treatment facility.
Such an aqueous suspension based lime delivery system also requires that the suspension contain a sufficiently high proportion of lime to make the transportation of the slurry economically cost effective. Otherwise, this technique bears the cost of transporting excessive amounts of water.
However, it is believed also desirable to be able to apply the treated biological particulates resulting from sewage treatment to agricultural soils because doing so would both make available an inexpensive source of organic materials, while providing for the inexpensive, non-polluting disposal of the solid products of the sewage treatment facility. Unfortunately, however, prior lime slurries contain materials which are added to maintain the lime in suspension, but are harmful or of no benefit to the soil agronomy. Such undesirable materials include metals, such as sodium, or other inorganic materials which form harmful inorganic salts, and also organic compounds having unknown consequences to plant and animal life. Such a material is disclosed in U.S. Pat. No. 4,849,128.
It is therefore an object and purpose of the present invention to provide a material which not only provides a stable lime slurry which is easily and conveniently handled, stored and applied to the sewage treatment process, but also is economically cost effective and, most importantly, results in a product which is agriculturally and environmentally friendly when applied or spread upon agricultural land as a fertilizer.
It is an object and feature of the invention to use materials in the lime treatment composition which are both effective in maintaining a sufficiently stable and concentrated lime slurry so as to be economically feasible, while also contributing to the nutrient condition of soil so that application of the products of the sewage treatment facility to soil for agricultural purposes becomes safe, legally permissible and desirable.
It is a further object and feature of the invention to provide a material which eliminates the need for investment in the installation of additional equipment in sewage treatment facilities by providing a lime slurry composition, which requires only that it simply be pumped into existing sewage treatment lagoons and blended with modest agitation.